Kims are megalomaniacs... and they may be stupid enough to do something irreversible... The problem is also North Korean society, they have been living too long in this propaganda, cut off from the outside, and brainwashed to love their leader. So even if Kim and his supporters were somehow eliminated the society may choose to reelect similar douchebags to power.
I remember, when I was a kid I was shown some videos at school, videos that came from North Korea that were showing some parades and festivities done to appreciate "the beloved leader". This was huge stuff, imagine thousands of people dancing in harmony, doing all these synchronized movements, shapes that are visible on a mass of people if you look from above etc. Such things are not really done in the West, not on such scale - they are too expensive, you would have to pay too much too the performers. The Koreans were doing it for free. For the enjoyment of their leader. (Well, some also probably out of fear that if they don't they'll be sent to some gulag).
Socialism and cult of one leader are things that devastate societies